Electromagnetic scattering from a structured slab comprised of periodically placed resistive cards
Jorgenson, Roy Eberhardt
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https://hdl.handle.net/2142/18926
Description
Title
Electromagnetic scattering from a structured slab comprised of periodically placed resistive cards
Author(s)
Jorgenson, Roy Eberhardt
Issue Date
1989
Doctoral Committee Chair(s)
Mittra, Raj
Department of Study
Electrical and Computer Engineering
Discipline
Electrical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Electronics and Electrical
Language
eng
Abstract
The structured slab, which is constructed by arranging cells composed of thin, lossy, dielectric cards on a one- or two-dimensional lattice, is an important material in the aerospace industry because of its high strength-to-weight ratio. Recently, the structured slab has also been used to reduce the radar cross section of various aircraft. It is important, therefore, to characterize how an electromagnetic wave scatters from this slab. The structured slabs discussed in this thesis are constructed by repeating lossy strips periodically in one dimension or lossy plates in two dimensions.
An electric field integral equation is formulated which has as its unknown the electric current flowing in a single unit cell of the structure. The periodicity of the structure is accounted for by using an efficiently calculated periodic Green's function. The loss is modeled by the resistive boundary condition. The integral equation is solved by the method of moments using subdomain basis functions. The generalized scattering matrix is calculated and the propagating reflection coefficients are plotted as a function of frequency for various structures.
The oblique scattering from one-dimensional arrays of strips is examined for various configurations of unit cells and various resistances. A depolarizing effect of the structure is found to be a function of incident angle and symmetry in the unit cell. The reflection from two-dimensional arrays of plates connected to form slabs of zigzag plates and honeycombs is also examined. The symmetry of the honeycomb unit cell minimizes the coupling between the TE and TM polarizations.
The structured slab is usually very thick in terms of wavelengths so that the incident electromagnetic energy can be absorbed effectively. To solve a thick structure in a straightforward manner requires too many unknowns; therefore, the final subject discussed in this thesis is how to extrapolate the scattering characteristics of a thick slab from the solution of a thin slab. Three methods are examined: cascading the generalized scattering matrix of a thin slab, which cannot account for currents flowing between the thin slabs; finding the modes in a lossy structure and mode matching, which is numerically intensive; using a few basis functions to model the interior current in a thick slab. The basis functions are constructed through the application of Prony's method.
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